JPH08263759A - Shoplifting preventing device - Google Patents

Abstract

PURPOSE: To discriminate to report which gate shoplifting occurs at by alternately transmitting detection signals to be transmitted from two transmitting antennas and alternately and independently judging received signals on the receiving side synchronously with their transmission. CONSTITUTION: A CPU 9a on the 1st gate side and a CPU 9b on the 2nd gate side time-dividedly send detection signals respectively through 1st and 2nd transmitting antennas 1a, 1b. A receiving antenna 3 alternately receives both the detection signals, a CPU 21a executes only 1st article detection processing and a CPU 21b executes only 2nd article detection processing. Detection results are reported by lamps 55a, 55b respectively. Thus which gate shoplifting occurs at is distinguishably detected and reported.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for preventing shoplifting, and in particular, a resonance circuit having a predetermined resonance frequency as an object to be detected is previously attached to a product or the like, and the resonance circuit is used as a doorway or the like. The present invention relates to a shoplifting prevention device that electrically detects the existence of a shoplifting action and notifies the occurrence of shoplifting.

[0002]

2. Description of the Related Art Conventionally, as this type of device, for example, a transmitting antenna and a receiving antenna are installed on both sides of a doorway of a library or a store that sells a predetermined product, and the device is preliminarily attached to a rental item or a product. Radio waves (detection signal) that have the same frequency as the resonance frequency of the resonance circuit (object to be detected)
Has been put into practical use, in which the occurrence of shoplifting is detected by detecting the signal level of the radio wave (received signal) received by the receiving antenna. That is, in this type of device, the resonance circuit attached to the product resonates, and based on the level change of the reception signal accompanying absorption and emission of the energy of the detection signal, the resonance circuit is provided between the transmission antenna and the reception antenna. It is determined whether or not there is a product attached with, and when it is determined that the product is present, a buzzer sounds or a lamp is lit to notify the occurrence of shoplifting.

In this type of shoplifting prevention device, the output of the radio wave emitted from the transmitting antenna is legally limited, and since noise is not erroneously detected as a change in the level of the received signal, the receiving sensitivity is also increased. It is moderately suppressed.
In order to reliably receive this relatively weak radio wave as a received signal, the distance from the transmitting antenna to the receiving antenna is limited to about 1.8 m, for example. This 1.
A distance of 8 m is sufficient for a person to pass through, but in a store or the like with a wide entrance / exit, two sets of the transmitting antenna and the receiving antenna (hereinafter referred to as a gate) are
They will be installed adjacent to each other.

[0004]

When two sets of gates are installed in this way, when a shoplifting action occurs, it is not possible to know which gate caused the shoplifting action. That is, when a product is present in one of the gates, the level of the reception signal of the reception antenna of that gate changes, but the reception antenna of the adjacent gate of the other side also receives the signal, and both gates receive it. Buzzer or lamp will be used for notification.

When there is a passerby at only one of the gates when this notification operation is performed, it is possible to detect it.
If there are people at both gates, the true criminal can escape,
It could catch innocent customers. The present invention has been made in view of these problems, and when a plurality of gates are provided, it is possible to detect the occurrence of a shoplifting act and to accurately identify and notify which gate the shoplifting occurred. The purpose is to provide a protection device.

[0006]

In order to achieve the above object, the present invention as set forth in claim 1, is, as illustrated in FIG. 1, a first transmitting antenna and a second transmitting antenna which are installed at a predetermined interval. A transmitting antenna, a receiving antenna installed in the center of the first transmitting antenna and the second transmitting antenna, and a detection signal of a frequency according to the command when receiving a predetermined command, the first transmitting antenna and the second transmitting antenna. First transmitting means and second transmitting means to be sent from the antenna respectively, synchronizing signal generating means for generating a synchronizing signal at a fixed cycle preset as a detection cycle, and the constant value each time the synchronizing signal is received. Until the synchronization signal is received again, the frequency of the detection signal is changed in a change pattern within a predetermined frequency range during a sweep time preset as a time shorter than 1/2 of the cycle In the time zone, the first frequency control means for issuing a command to the first transmission means to stop the transmission of the detection signal, and the reception signal from the reception antenna during the sweep time each time the synchronization signal is received. First article detecting means for determining whether or not there is an article having a resonance circuit whose resonance frequency is set within the frequency range between the first transmitting antenna and the receiving antenna, based on the signal level of A first notification means for notifying that the first article detection means determines that the article is present; and a permission signal generation means for generating a permission signal when the sweep time has elapsed after receiving the synchronization signal. Every time the permission signal is received, the frequency of the detection signal is changed in a change pattern within a predetermined frequency range during the sweep time, and then the permission signal is received again. In the inter-band, the second frequency control means for issuing a command to the second transmitting means to stop the transmission of the detection signal, and the reception signal from the reception antenna during the sweep time after receiving the permission signal. Second article detecting means for determining whether or not there is an article having a resonance circuit whose resonance frequency is set within the frequency range between the second transmitting antenna and the receiving antenna based on the signal level of And second notifying means for notifying that the second article detecting means determines that the article is present.

The invention described in claim 2 is the same as claim 1
In the shoplifting prevention device according to claim 1, when the first article detecting means receives the synchronization signal, first level detecting means for detecting a signal level of the received signal at predetermined intervals during the sweep time, First storage means for sequentially storing each signal level detected by the first level detection means, and the first storage means
First average value calculation means for reading out the signal level for a predetermined detection cycle stored in the storage means and calculating each average value of the signal levels detected at the same time in each detection cycle, and the first average value calculation It is determined whether or not the article is present based on the average value calculated by the means, and when it is determined that the article is present, a first determination means for causing the first informing means to perform an informing operation, and When the second article detecting means receives the permission signal, during the sweep time,
Second for detecting the signal level of the received signal every predetermined time
Level detection means, second storage means for sequentially storing each signal level detected by the second level detection means, and signal levels for a predetermined detection cycle stored in the second storage means are read out to detect each of the above detections. Second average value calculating means for calculating each average value of the signal levels detected at the same time in the cycle, and whether or not the article exists based on the average value calculated by the second average value calculating means. And a second determination means for causing the second notification means to perform a notification operation when it is determined that the article is present.

Further, the invention described in claim 3 is the same as claim 2
In the shoplifting prevention device described in (1), the first level detecting means and the second level detecting means respectively include a first oscillator and a second oscillator capable of controlling an oscillation frequency, and oscillations from the first oscillator and the second oscillator. A first signal for mixing a signal and the received signal to convert the frequency of the received signal to a different frequency;
The frequency converter and the second frequency converter, and the first oscillator and the second oscillator, respectively, so that the frequency of the received signal converted by the first frequency converter and the second frequency converter is always a predetermined measurement frequency. The first frequency conversion control means and the second frequency conversion control means for controlling the oscillation frequencies of the two oscillators, and the cycle in which the frequency of the detection signal sent by the first frequency control means and the second frequency control means is changed. And a second detection means for detecting the signal level of the output signal from the frequency conversion means as the signal level of the received signal in each of the detection cycles. And

[0009]

In the shoplifting prevention device according to claim 1 configured as described above, the first transmitting antenna and the second transmitting antenna are installed at a predetermined interval, and the center of both transmitting antennas is installed. The receiving antenna is on. The synchronization signal generating means is configured to have a preset fixed cycle (hereinafter,
A sync signal is generated in a detection cycle.

Each time the first frequency control means receives the synchronization signal, the frequency of the detection signal generated by the first transmission means is changed in a predetermined frequency range during a preset sweep time. When the sweep time has been changed, the sending of the detection signal is stopped. This sweep time is preset as a time shorter than 1/2 of the detection cycle. That is, a detection signal whose frequency is changed is emitted from the first transmitting antenna during the sweep time from the detection of the synchronization signal. Further, the permit signal is generated by the permit signal generating means when the sweep time has elapsed since the synchronizing signal was generated.

Then, the second frequency control means changes the frequency of the detection signal generated by the second transmission means in a change pattern within a predetermined frequency range during the sweep time each time the permission signal is received. When the sweep time has elapsed, the transmission of the detection signal is stopped. That is, the detection signal whose frequency is changed is emitted from the second transmitting antenna during the sweep time from the reception of the permission signal.

Therefore, the detection signal from the first transmitting antenna and the detection signal from the second transmitting antenna are alternately transmitted without temporal overlap. On the other hand, when the first article detecting means receives the synchronization signal, there is an article having a resonance circuit in which the resonance frequency is set within the frequency range based on the signal level of the received detection signal during the sweep time. Or not. If it is determined that the article is present, the first notification means performs the notification operation. That is, the presence or absence of the article is determined in synchronization with the transmission signal transmitted from the first transmitting antenna, and when the article is present, a notification is made to notify that shoplifting has occurred. Since the detection signal received during the sweep time from the reception of the synchronization signal used for this determination is sent from the first transmitting antenna, the article detected by the first article detecting means is the receiving antenna. And the first transmitting antenna (hereinafter referred to as the first gate).

Further, when the second article detecting means receives the permission signal, the second article detecting means operates the resonance circuit whose resonance frequency is set within the frequency range based on the signal level of the reception signal from the reception antenna during the sweep time. It is determined whether or not there is an article that the user has. If it is determined by this determination that the article is present, the second notification means performs the notification operation. The detection signal received during the sweep time from the reception of the permission signal, which is used for this determination, is the one sent from the second transmitting antenna, so that the article detected by the first article detecting means is the second article. It is located between the transmitting antenna and the receiving antenna (hereinafter referred to as the second gate).

Therefore, in the shoplifting prevention device according to the first aspect of the present invention, the detection signal to be transmitted is alternately transmitted by the two transmitting antennas, and the receiving side also determines alternately and independently of each other in synchronization with the transmission. In addition, since the synchronization signal, which is the reference of the detection signal transmitted from the first transmitting antenna, is also received and the determination processing for one is performed in synchronization with this, it is possible to identify which gate the shoplifting occurred. Can be detected. Further, since the first notifying means and the second notifying means are provided corresponding to the respective article detecting means and the judgment result by each article detecting means is independently notified, which gate is used by a user such as a store owner. It is possible to distinguishably notify whether shoplifting has occurred. Therefore, people who have shoplifted can be properly detected.

Next, in the shoplifting prevention device according to the second aspect, the first level detecting means provided in the first article detecting means detects the signal level of the received signal at every predetermined time during the sweep time. To do. The first storage means sequentially stores the detected signal level. In this way, when the signal level for the predetermined detection period is stored in the first storage means, the first average value calculation means calculates each average value of the signal levels detected at the same time within each sweep time. Then, based on the average value, the first determination means determines whether or not an article exists, and when it is determined that the article exists, the first
The notification means is caused to perform the notification operation.

The second article detecting means, like the first article detecting means, also includes a second level detecting means, a second storing means, a second average value calculating means, and a second determining means, and the second article concerned. Substantially similar processing corresponding to the detection means is performed. Since the processing performed by the first article detecting means described below is similarly performed by the second article detecting means, the processing of the first level detecting means, the first storing means, etc. will be represented. First level detecting means (second level detecting means) ". This is also true in the second level detecting means.
It means that the same processing as the first level detecting means is performed or the corresponding operation is performed.

That is, in the shoplifting prevention device according to the second aspect, the first level detecting means (second level detecting means) samples the signal level of the detection signal within the sweep time for receiving the detection signal, and performs the first storage. The data is stored in the means (second storage means). Then, when a signal level for a predetermined detection period (a predetermined number of data strings when the signal level for one sweep time is counted as one data string) is stored, a first average value calculation means (second
The average value calculation means) reads out the signal level at the same time in each detection cycle and calculates the average at each time. First transmitting antenna (second transmitting antenna) based on each average value
It is determined whether or not there is an article having a resonance circuit between the antenna and the receiving antenna.

Therefore, according to the shoplifting prevention device of the present invention,
Even if random noise occurs within the frequency range in which the frequency of the detection signal is changed (in the frequency band of the detection signal), the average value of the calculated reception level does not have a significant effect. In the case where the resonance circuit exists over a plurality of time zones in the detection cycle, the signal level at the time corresponding to the detection signal of the same frequency fluctuates greatly over the time zone, and the average value thereof also It greatly changes from the steady value. Therefore, in order to detect the resonance circuit over a plurality of detection cycles, the detection cycle is sufficiently short compared to the time required for a person to pass between the transmitting and receiving antennas (for example,
If it is set for several ms, only the presence of a person having a resonant circuit can be accurately detected. Therefore, according to the shoplifting prevention device of the second aspect, in addition to the effect of the invention of the first aspect, the occurrence of the shoplifting action is always accurately detected and notified without being affected by random noise. You can

Further, in the shoplifting prevention device according to the third aspect, when the signal level of the detection signal is detected by the first level detecting means (second level detecting means), the first frequency converting means (second frequency The conversion means mixes the transmission signal from the first oscillator (second oscillator) whose transmission frequency can be controlled with the detection signal received by the receiving antenna, and converts the frequency of the detection signal into a different frequency. And the first frequency conversion control means (second frequency conversion control means) so that the frequency of the detection signal converted by the first frequency conversion means (second frequency conversion means) is always the predetermined measurement frequency. The oscillation frequency of the oscillator (second oscillator) is controlled, and the first detection means (second detection means) controls the signal level of the output signal from the first frequency conversion means (second frequency conversion means) as a detection signal. Detect as signal level That.

That is, in the shoplifting prevention device according to the third aspect of the present invention, the reception level is detected after converting the frequency of the detection signal that periodically changes according to the frequency change of the detection signal into a constant measurement frequency. The so-called heterodyne system is adopted. Therefore, according to the shoplifting prevention device of claim 3, in addition to the effect of the invention of claim 2, the reception level in the entire frequency range in which the frequency of the detection signal is changed (that is, the frequency band of the detection signal). Without detecting
Since the reception level can be detected only for the frequency of the detection signal actually transmitted at that time, it is possible to minimize the influence of external noise, and more accurately determine the presence or absence of an article having a resonant circuit. Can be determined.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. First, FIG. 2 is a block diagram showing the configuration of the shoplifting prevention device of the embodiment. As shown in FIG.
The shoplifting prevention device of this embodiment has a predetermined resonance frequency f0 (f0 = 8.23 MH in this embodiment) in a store selling video tapes, music compact discs, and the like.
LC resonance circuit Ma1 or resonance circuit M having z)
a2 is preliminarily attached to the article M1 or article M
2 detects the passing of the vicinity of a specific doorway and notifies the occurrence of shoplifting, and the first transmitting antenna 1a and a first transmission antenna 1a installed at the doorway at a predetermined interval (for example, 3.6 m). The second transmission antenna 1b, the reception antenna 3 installed between the two transmission antennas 1a and 1b, and a predetermined frequency range f1 to f2 including the resonance frequencies f0 of the resonance circuits Ma1 and Ma2 (f1 = 7. 38 MH
z to f2 = 9.07 MHz),
A first transmitting device 5a and a second transmitting device 5b which are respectively transmitted from the first transmitting antenna 1a and the second transmitting antenna 1b.
And a receiving device 7 that detects and notifies the occurrence of shoplifting based on the detection signal received by the receiving antenna 3.

The resonance circuit Ma1 and the resonance circuit Ma2
Is formed on a dedicated tag called a tag, a price tag of a product, or the like, and then attached to the article M1 and the article M2, respectively. The space sandwiched between the first transmitting antenna 1a and the receiving antenna 3 is called a first gate, and the space sandwiched between the second transmitting antenna 1b and the receiving antenna 3 is called a second gate.

The first transmitter 5a includes a CPU, a ROM, and an R.
Microcomputer equipped with AM, etc. (hereinafter simply referred to as CP
9a and a frequency data (digital data) output from the CPU 9a, a predetermined frequency range (f
Direct digital synthesizer (hereinafter simply referred to as DDS) 11a that outputs a sine wave signal of 1 to f2)
A low-pass filter (LPF) 13a for removing unnecessary harmonic components from the output signal of the DDS 11a, a variable attenuator 15a for attenuating the level of the signal output from the low-pass filter 13a, and an output signal of the variable attenuator 15a. An amplifier (AMP) 17a that amplifies and sends out as a detection signal from the first transmission antenna 1a. The attenuation value of the variable attenuator 15a is set so that the output level of the detection signal transmitted from the first transmitting antenna 1a falls within a prescribed value.

The second transmitting device 5b has substantially the same structure as the first transmitting device 5a. That is, CPU
9b, DDS 11b, low-pass filter 13b,
A CPU provided with a variable attenuator 15b and an amplifier 17b.
Except for 9b, the first transmitter 5a has substantially the same operation as the corresponding configuration.

On the other hand, the receiving device 7 has a CPU and an RO, respectively.
A microcomputer (hereinafter, simply referred to as CPU) 21a, 21b provided with M, RAM and the like, and a bandpass filter for inputting a reception signal from the reception antenna 3 and attenuating frequency components other than the reception band (f1 to f2). (BP
F) 23, an amplifier (AMP) 25 for amplifying the received signal from the bandpass filter 23, a variable attenuator 27 for attenuating the amplified received signal level according to a control voltage from the outside, and a CPU 9a. When the falling edge of the sync signal (described later) is detected, the frequency data (digital data) input by the CPU 21a is output, and the CPU 2
When a falling edge of a permission signal (described later) from 1a is detected, a switching circuit (hereinafter, referred to as SW) 28 that outputs frequency data (digital data) input by the CPU 21b, and the frequency data output from SW28 Predetermined frequency range (in the present embodiment, 18.08 to 19, higher than the frequency of the detection signal by 10.7 MHz).
(77 MHz) sine wave signal, DDS 29 as an oscillator, amplifier (AMP) 31 for amplifying the output signal from DDS 29, and the output signal of the amplifier 31 are input to obtain necessary frequency components (18.08 to 19). .77 MHz)
Band pass filter (BPF) 33 that allows only
And the output signal from the bandpass filter 33 and the received signal from the variable attenuator 27 are mixed to obtain a received signal of 10M.
Hz band (in this embodiment, intermediate frequency fi = 10.7 MH
mixer 3 as a frequency conversion means for converting the signal of FIG.
5, an IF bandpass filter (IF-BPF) 37 that inputs the received signal from the mixer 35 and attenuates frequency components other than the intermediate frequency fi, and an IF amplifier that amplifies the output signal from the IF bandpass filter 37. (IF-A
MP) 39, a detector 41 that detects the amplified received signal, a high-pass filter (HPF) 43 and a low-pass filter (LPF) 45 that shape the detected voltage signal output from the detector 41, and a low-pass filter. The A / D converter 47 which converts the waveform-shaped detected voltage signal output from the digital signal 45 into a digital signal and outputs the digital signal to the CPUs 21a and 21b, and the 10.7 MHz reception output from the IF amplifier 39 to the detector 41 Diode 49 for detecting the signal
And an automatic gain control circuit that outputs a control voltage to the variable attenuator 27 so that the detection voltage from the diode 49 always becomes the predetermined reference voltage V and keeps the level of the received signal input to the detector 41 constant. 51 and a lamp 55 as a first informing means for informing the occurrence of shoplifting at the first gate
a and a buzzer 57a, and a lamp 55b and a buzzer 57b as second notification means for notifying occurrence of shoplifting at the second gate.

The variable attenuator 27, the diode 49,
The control loop including the automatic gain control circuit 51 is
This is for stabilizing the overall level of the received signal input from the amplifier 39 to the detector 41 to a level that can be detected by the detector 41, and has a sharp level change (for example, a change of 1 KHz or more) in the received signal. ) Is not set to follow.

The first transmitter 5a and the receiver 7 are connected by a cable 59a, and the second transmitter 5b and the receiver 7 are connected by a cable 59b. In the shoplifting prevention device of the present embodiment configured as described above, the CPU 9a of the first transmitting device 5a executes the first sweeping process (FIG. 3) described later, whereby the first transmitting antenna 1a.
To f1 = 7.38 MHz to f2 = 9.07 MHz, the detection signal is swept and transmitted. Also, the second transmitter 5b
The CPU 9b executes a second sweep process (FIG. 8) described later to sweep and send the same detection signal from the second transmitting antenna 1b. Then, the CP of the receiving device 7
U21a detects the signal level of the detection signal received by the receiving antenna 3 by executing a first article detection process (FIG. 4) described later, and based on the signal level, the presence or absence of shoplifting at the first gate is detected. Detect and C of receiving device 7
The PU 21b detects the signal level of the detection signal received by the receiving antenna 3 by executing the second article detection process, and detects the presence or absence of shoplifting at the second gate based on the signal level.

Therefore, first, the CPU 9 of the first transmitter 5a
The first sweep process executed by a will be described with reference to FIG. It should be noted that this first sweep process is repeatedly executed at all times when the first transmitter 5a is powered on. FIG.
As shown in, when the execution of the first sweep process is started, first, at step (hereinafter simply referred to as S) 110, 1.7 m
After waiting for s, a synchronization signal is output in the following S120.
This synchronizing signal is generated by setting the voltage level of one output terminal of the CPU 9a to High for a short time (0.1 ms in this embodiment). The voltage level of this output terminal is assumed to be Low when the power of the first transmitter 5a is turned on. In the shoplifting prevention device of this embodiment, the synchronization signal is sent to the CPU 21 via the cable 59a.
a and SW28.

When the sync signal is issued in this manner, the subsequent S
At 130, the frequency data to be output to the DDS 11a is initialized to f1 (= 7.38) which is the minimum value of the sweep range.
The frequency data representing (MHz) is output during the time Δt.
Δt is the length of one step when the frequency of this detection signal is changed stepwise, and Δt = 1.6 ms / 80 = 20 μ
It is set to s.

Then, in the first transmitter 5a, the DD
From S11a, the sine wave signal of 7.38MHz is 20μs
This sine wave signal is output during the low pass filter 1
3a, the variable attenuator 15a, and the amplifier 17a,
It is transmitted as a detection signal from the first transmitting antenna 1a.
In this embodiment, the DDS 11a, the low-pass filter 13a, the variable attenuator 15a, and the amplifier 17a are the first
It corresponds to the transmission means.

When 20 μs has elapsed, the subsequent S1
At 40, the process as the first frequency control means for setting the next frequency data and outputting it to the DDS 11a is executed. Here, in the present embodiment, the frequency of the detection signal is f1
From 7.38 MHz to f2 = 9.07 MHz, 1.
It takes 6 ms to increase in 80 steps. Therefore, as the next frequency data output in S140, the frequency Δf (Δf = (f2−f1) / 79 = 2) per step is added to the frequency of the detection signal currently transmitted.
1.392 KHz) is added to set the data representing the frequency.

Then, wait for 20 μs at S150,
In subsequent S160, the frequency data currently output to the DDS 11a is f2 (= 9.0, which is the maximum value in the sweep range).
(7 MHz) is determined. If it is determined in S160 that the frequency data has not reached the value indicating f2, the process returns to S140 and DD
The updating of the frequency data to S11a (S140) and the waiting time Δt per step (S150) are repeated.

In this way, the frequency data to the DDS 11a is updated by Δf each time Δt elapses, and when it is determined in S160 that the currently output frequency data has reached the value representing f2. , S170, the output of the frequency data is stopped, and then the process returns to S110.

Then, the DDS 11a receives S110 and S
Time to wait at 120 (1.7ms + 0.1ms =
The output of the sine wave signal is stopped only for 1.8 ms), and the transmission of the detection signal is stopped for 1.8 ms. Then, when 1.8 ms has elapsed, S12 is again set.
The processing from 0 to S160 is executed, the synchronization signal is output, and the frequency of the detection signal changes from f1 to Δt.
Every time (= 20 μs) elapses, Δf (= 21.392K
Hz) each time, and again rises to f2.

In other words, the execution of this first sweep process causes the detection signal to be 1.7 ms, as shown in FIG. 6 (A).
Transmission stop period (S110 and S160), 0.1 ms (S120) for synchronizing signal output, and 7.38M
The sweep period (S130 to S150) of 1.6 ms in which the frequency is increased from 80 Hz to 9.07 MHz in 80 steps makes a total of 3.4 ms, which is transmitted from the first transmitting antenna 1a. Hereinafter, this period of 3.4 ms is referred to as a detection period.

Next, the first article detection process executed by the CPU 21a of the receiving device 7 will be described with reference to FIG.
As shown in FIG. 4, when the execution of the first article detection process is started, first, in S210, the inside of the CPU 21a is initialized. Then, in subsequent S220, the transmission frequency of the DDS 29 is changed in synchronization with the detection cycle on the side of the first transmission device 5a, thereby converting the frequency of the reception signal from the reception antenna 3 into the intermediate frequency fi, and the frequency The first data acquisition process for detecting the converted signal level is executed as follows.

That is, first, in S410, it is determined whether the synchronization signal sent from the CPU 9a of the first transmitter 5a has fallen from the high level to the low level. If it has not fallen, it returns to S410 again and repeats this loop to wait until it falls.

If it is determined in S410 that the sync signal has fallen, the process proceeds to S420, where S
The frequency data to be output to the DDS 29 via W28 is initialized to 18.08 which is the minimum value of the frequency change range.
Output frequency data representing MHz (= f1 + fi),
Then, in S430, wait for 20 μs.

Then, from the DDS 29, 18.08M
The sine wave signal of Hz is output for 20 μs, and this sine wave signal is input to the mixer 35 via the amplifier 31 and the bandpass filter 33. Then, at this time, as described above, 7.38 MH from the first transmitting antenna 1a.
Since the detection signal of z is transmitted, the reception signal from the reception antenna 3 is frequency-converted into a signal of 10.7 MHz by the mixer 35 in the reception device 7, and then the IF bandpass filter 37 and the IF amplifier 39 are used. The detected voltage from the detector 41 is inputted to the detector 41 via the high-pass filter 43 and the low-pass filter 45, and then output from the A / D converter 47.

Then, in the subsequent S440, the CPU 21a fetches the digital data (hereinafter referred to as level data) from the A / D converter 47 and stores it in the RAM, and first detecting means (first level detecting means) and The processing as the first storage means is executed, and in the subsequent S450, the next frequency data is set and output to the DDS 29 via the SW28,
The processing as the first frequency conversion control means is executed.

The next frequency data set in S450 is also the same as in S130 of the first sweeping process executed by the first transmitter 5a, at the frequency of the sine wave signal currently output by the DDS 29. This is data representing the frequency obtained by adding the frequency Δf (= 21.392 KHz) per step in the first sweep processing.

Then, in the subsequent S460, it is determined whether 80 level data have been fetched, that is, whether the process of S440 has been performed 80 times. If it is determined that 80 level data have not been fetched, In the subsequent S470, after waiting for a time Δt (= 20 μs) per step in which the frequency of the detection signal is changed by the first sweep processing, S
Returning to 440, the processing of S440 to S470 is repeated.
On the other hand, if it is determined in S460 that 80 level data have been fetched, the process proceeds to S470 and a permission signal is output. This permission signal is issued when a sufficient time (for example, 1.61 ms) to capture 80 pieces of level data has elapsed from the detection of the falling edge of the synchronization signal in S410, and the voltage level of one output terminal of the CPU 21a is changed for a short time. It is generated by making High (0.1 ms in this embodiment) only. The voltage level of this output terminal is
It is assumed to be Low when the power of the receiving device 7 is turned on. When the permission signal is output in this way, the first data fetching process is ended.

That is, in the first data fetching process, by detecting the fall of the synchronizing signal, it is detected that the sending of the detection signal is started immediately thereafter (S41).
0), for 20 μs from that timing, DDS29
The transmission frequency of the DDS 29 is maintained at 18.08 MHz (= f1 + fi) (S420, S430), and thereafter, the transmission frequency of the DDS 29 is changed to Δt.
Every time (= 20 μs) elapses, Δf (= 21.392K
Hz), and finally 19.77 in 80 steps.
The frequency is increased to MHz (= f2 + fi) (S450 to S470). Therefore, from DDS29,
A sine wave signal whose frequency is higher than that of the detection signal by fi (= 10.7 MHz) is always output, and the reception signal from the reception antenna 3 is always converted into a signal of intermediate frequency fi = 10.7 MHz. Will be input to the detector 41.

Further, in the first data fetching process, D
Just before increasing the transmission frequency of DS29 by Δf,
The signal level (detection voltage) of the reception signal detected by the detector 41 is fetched as level data via the A / D converter 47, and each level data is sequentially stored in the RAM (S440). .

Therefore, when the first data fetching process is executed once after the power is turned on, 80 pieces of level data D1.1, D1.multidot. Are stored in the RAM as shown in the uppermost stage of FIG. 6B. 2,
..., D1 79 and D1 80 are stored. In FIG. 6 (B), D1 · n indicates that the frequency of the detection signal transmitted from the first transmitting antenna 1a is “(f1 + (n−1)”.
.DELTA.f): However, n represents the level data when it is an integer of 1-80.

Then, the permission signal is generated every time the first data fetching process is completed once. Next, the CPU 21a
When the execution of the first data acquisition process is completed, it is determined in S230 of FIG. 4 whether or not the first data acquisition process has been executed 16 times. If it is determined that the first data acquisition process has not been executed 16 times, , S220, and the processes of S220 and S230 are repeated.

Then, when it is determined in S230 that the first data acquisition process has been executed 16 times, the process proceeds to S240. Therefore, when proceeding to S240, a total of 1280 (= 80 × 16) level data are stored in the RAM as shown in FIG. 6B. In FIG. 6B, Dm · n represents the nth level data captured when the m-th (m-th sweep) first data capture process is executed.

Next, in S240, a predetermined counter n
Is reset to "0", and in the subsequent S250, the counter n
Is incremented. Then, in the subsequent S260, each of the data fetching processes executed 16 times as described above is performed n times.
Secondly, the level data Dm · n (m = 1 to 1) stored in the RAM
The process as the first average value calculating means for calculating the average value Dn of 16) is executed.

Then, in the following S270, it is determined whether or not the value of the counter n has reached 80, that is, whether or not the calculation of the average value has been completed for all the 1st to 80th level data, and the counter is counted. When it is determined that the value of n is not 80, the process returns to S250 and S250 to S270.
Is repeated. Then, in S270, the counter n
When it is determined that the value of 80 has reached 80, the process proceeds to S280, and all the average values D1 to D8 calculated in S260.
Store 0 in RAM.

Therefore, when the processing of S280 ends, R
As shown at the bottom of FIG. 6B, the AM has level data detected at the same timing in each of the 16 data acquisition processes (that is, the reception level when the detection signal of the same frequency is transmitted). ) Averaged 80 values (hereinafter,
D1 to D80 will be stored.

Then, in S290, calculated as 80
It is determined whether or not there is data outside a preset predetermined range among the average data D1 to D80.
When the process as the determination means is executed and the data out of the predetermined range is present, the lamp 55a and the buzzer 57a are driven for one second only in S300 to confirm that the article M1 is present in the first gate. Notify (warn). Note that S2
The predetermined range used in the determination of 90 is, as illustrated in FIG. 7B, the upper limit set by a predetermined value larger than the value of the average data calculated when the article M1 does not exist in the first gate. The value VthH and, conversely, the lower limit value V set to be smaller than the value of the average data by a predetermined value.
It is a range between thL, and in S290, if any one of the 80 average data D1 to D80 exceeds the upper limit value VthH or falls below the lower limit value VthL, it is determined that the article M1 exists. To do.

When the process of S300 is executed, or when it is determined that there is no average data outside the predetermined range in S290, the process proceeds to S310, and among the level data stored in the RAM. Oldest 1
Data for the sweep cycle, that is, 80 level data D1.1-D1-80 stored in the first data acquisition processing is deleted, and each level data stored in the mth data acquisition processing Level data D (m-1) ・ 1 to D (m-1) that stores Dm ・ 1 to Dm ・ 80 in the (m-1) th data loading process.
・ Restore in RAM as 80, and in subsequent S320, S
Just as in the case of 220, the first data fetching process shown in FIG. 5 is executed. The 80 level data stored in the RAM in the first data fetching process executed in S320 are stored in the RAM as the latest level data D16-1 to D16.80.

Then, when the execution of the first data fetching process is completed in S320, the process returns to S240 again and S2
The processing of 40 to S320 is repeated, and thereafter, every time 80 pieces of level data for one detection cycle are captured, the total of the level data for that time and the level data for the 15 sweep cycles immediately before that is summed. Average data D1 to D80 are calculated using the level data for 16 sweep cycles, and the presence or absence of the article M1 is sequentially determined using the average data D1 to D80.

Next, the second sweep process executed by the CPU 9b of the second transmitter 5b will be described with reference to FIG.
It should be noted that this second sweep process is executed repeatedly whenever the second transmitter 5b is powered on, and the waveform of the detection signal generated in the second sweep process is the same except for the phase. The values of f1, f2, and Δt are the same as the values in the first sweep process because they are exactly the same as the waveform of the detection signal generated in the one sweep process.

As shown in FIG. 8, when the execution of the second sweep process is started, first, in S510, the CPU 21a waits for the fall of the permission signal, and then in S520, DD
The frequency data to be output to S11b is initialized, and the frequency data representing f1, which is the minimum value of the sweep range, is set at time Δt.
Output during.

Then, in the second transmitter 5b, the DD
From S11b, 7.38MHz sine wave signal is 20μs
This sine wave signal is output during the low pass filter 1
3b, the variable attenuator 15b, and the amplifier 17b,
It is sent out as a detection signal from the second transmitting antenna 1b.
In the present embodiment, the DDS 11b, the low pass filter 13b, the variable attenuator 15b, and the amplifier 17b are the second
It corresponds to the transmission means.

When 20 μs has elapsed, the subsequent S5
At 30, the process as the second frequency control means for setting the next frequency data and outputting it to the DDS 11b is executed. That is, as described above, similar to the first sweep process,
The frequency of the detection signal is changed from f1 = 7.38 MHz to f2 =
In order to raise to 9.07 MHz in 80 steps over 1.6 ms, as the next frequency data output in S530, the frequency Δf ( = 21.392 KHz) is added to set the data representing the frequency.

Then, in the subsequent S540, wait for 20 μs,
In subsequent S550, the frequency data currently output to the DDS 11b is f2 (= 9.0, which is the maximum value in the sweep range).
(7 MHz) is determined. If it is determined in S550 that the frequency data has not reached the value indicating f2, the process returns to S530 and the DD
The frequency data update to S11b (S530) and the time per step Δt wait (S540) are repeated.

In this way, the frequency data to the DDS 11b is updated by Δf each time Δt elapses, and when it is determined in S550 that the currently output frequency data has reached the value representing f2. , S560, the output of the frequency data is stopped, and then the process returns to S510.

Then, the DDS 11b stops outputting the sine wave signal for the time until the next fall of the permission signal is detected. As described above, the permission signal is transmitted for a predetermined time (for example, 1.61
Since it is a signal generated after the elapse of ms), it is generated with the same period of 3.4 ms as the synchronization signal. That is,
S520 to S56 after a predetermined time from the synchronization signal
The process up to 0 is executed, and the frequency of the detection signal is f1.
Therefore, every time Δt (= 20 μs) elapses, Δf (= 2
1.392 KHz) in increments of up to f2.

That is, the detection signal sent out in the second sweeping process is the graph shown in FIG. 6A delayed by a predetermined time. That is, the transmission stop period of 1.8 ms (S510 and S560), and 7.38M
The sweep period of 1.6 ms (S520 to S550) in which the frequency is increased in 80 steps from Hz to 9.07 MHz, which is a total of 3.4 ms, is transmitted from the second transmitting antenna 1b.

Corresponding to the second sweep processing, the receiving apparatus 7 side carries out the second article detection processing. It should be noted that, in the second article detection process, in FIG. 4 showing the above-described first article detection process, the CPU 21a may perform the process or may be symmetrical to the data storage performed in S220, S280, and S320. It is the same process except that it is not the CPU 21b. That is, the second article detection process is performed by replacing S260 with the second average value calculating unit, S290 with the second determining unit, and replacing the lamp 55a and the buzzer 57b driven in S310 with the lamp 55b and the buzzer 57b, respectively. Therefore, only the data fetching process (hereinafter referred to as the second data fetching process) performed in S220 and S320 will be described.

This second data fetching process is executed as shown in FIG. That is, first, in S610, the CPU 21a of the receiving device 7 waits for the fall of the permission signal. When it is determined in S610 that the sync signal has fallen and changed, the process proceeds to S620 and SW
The frequency data to be output to the DDS 29 via 28 is initialized to 18.08M which is the minimum value of the frequency change range.
Frequency data representing Hz (= f1 + fi) is output, and then waits for 20 μs in S430.

Then, from DDS 29, 18.08M
The sine wave signal of Hz is output for 20 μs, and this sine wave signal is input to the mixer 35 via the amplifier 31 and the bandpass filter 33. Then, at this time, as described above, 7.38 MH from the second transmitting antenna 1b.
Since the detection signal of z is transmitted, the detection signal received by the reception antenna 3 in the reception device 7 is the mixer 35.
After the frequency conversion to a signal of 10.7 MHz by
The detection voltage from the detector 41, which is input to the detector 41 via the F bandpass filter 37 and the IF amplifier 39,
The waveform is shaped by the high-pass filter 43 and the low-pass filter 45, and then output from the A / D converter 47.

Then, in the subsequent S640, the CPU 21b takes in the level data from the A / D converter 47 and stores it in the RAM, and serves as the second detecting means (second level detecting means) and the second storing means. And continue with S6
At 50, the process as the second frequency conversion control means for setting the next frequency data and outputting it to the SW 28 is executed.

The next frequency data set in S650 is also the frequency of the sine wave signal currently output by the DDS 29, just as in S530 of the second sweep process executed by the second transmitter 5b. This is data representing the frequency obtained by adding the frequency Δf (= 21.392 KHz) per step in the second sweep processing.

In subsequent S660, it is determined whether 80 level data have been fetched, that is, whether the process of S640 has been performed 80 times. If it is determined that 80 level data have not been fetched, In the following S670, after waiting for a time Δt (= 20 μs) per step in which the frequency of the detection signal is changed by the sweep process, S64 is performed.
The process returns to 0 and the processes of S640 to S670 are repeated. On the other hand, if it is determined in S660 that 80 level data have been captured, the data capturing process ends.

That is, the second data acquisition process is S610.
The process is the same as the first data fetch process except that the wait for the fall of the permission signal instead of the synchronization signal is waited for, and the generation process of the permission signal is not performed. In S610, the permission signal, not the synchronization signal, is detected and the process is started, so that the second data acquisition process is performed after a predetermined time (for example, 1.61 ms) with respect to the first data acquisition process. It will be. Further, since the second data acquisition process is delayed, the second article detection process is also delayed from the first article detection process by a predetermined time.

FIG. 10 is a timing chart showing the above time relationship. That is, FIG. 10A shows the CPU 9a.
1B is a synchronizing signal emitted from the first transmitting antenna 1a by the first sweeping process, and FIG.
0 (C) is a permission signal issued by the CPU 21a, as shown in FIG.
(D) shows a detection signal emitted from the second transmitting antenna 1b by the second sweep process.

That is, at time zero, the first transmitter 5a
When is activated, a synchronization signal is emitted for 0.1 ms after 1.7 ms as shown in FIG. Then, as shown in FIG.
As shown in (B), while the detection signal is 1.6 ms, the frequency f1
To f2 are changed stepwise. When a sufficient time (for example, 1.61 ms) for sending this detection signal has elapsed, a permission signal is issued for 0.1 ms as shown in FIG. 10 (C).
At this time, ε = 0.01 ms. When this permission signal falls, the detection signal is 1.6 m as shown in FIG.
During s, the frequency is changed stepwise from f1 to f2.
In addition, the synchronization signal of FIG. 10 (A) is 3.4 m as described above.
Since it is repeatedly transmitted with s as a cycle, FIG.
From the trailing edge of the first detection signal to the leading edge of the detection signal in FIG.
There is a margin of 1.7 + 0.1-0.1-1.6).

That is, as is apparent from this figure, the first
The detection signal transmitted from the transmission antenna 1a and the detection signal transmitted from the second transmission antenna 1b are transmitted from the respective transmission antennas which are alternately changed at a predetermined time interval. Therefore, the receiving antenna 3 for receiving these detection signals
Will alternately receive both detection signals. As described above, the CPU 21a performs only the processing relating to the detection signal of FIG. 10B, that is, the first article detection processing shown in FIG. 4, and the processing relating to the detection signal of FIG.
21b, the load on the CPUs 21a and 21b is small despite the large amount of data calculation processing described above.

That is, when 16 receiving signals of the detection signal of FIG. 10B are received by the receiving antenna 3, the processing as the first average value calculating means and the processing as the first recording means are performed.
These processes may be performed before the next detection signal in FIG. 10B is received. In terms of time,
The time from the fall of the detection signal of FIG. 10 (B) to the fall of the next synchronization signal (FIG. 10 (A)), that is, 1.8 ms (1.8 = 1.7 + 0.1) Therefore, even if the time of 0.1 ms for generating the permission signal in FIG. 10C is subtracted, it is still sufficient to perform the processing as the first average value calculation means and the processing as the first recording means. Therefore, it is not necessary to use an expensive high-speed CPU for the portion of the CPU 21b that performs the calculation. One CPU 2
In 1b, since it is not necessary to generate the permission signal,
Further, there is time to spare for processing.

Further, since the processing is synchronized for each cycle by using the synchronization signal, the CPUs 9a, 9b, 21a, 21b
It is not required that each clock oscillator, which is the basis of the operation timing of, also be highly accurate. That is, 4 oscillated
Even if there is a slight error between the two clocks, the processing of the first average value calculating means, the processing of the first recording means, etc. is performed in synchronization with the synchronization signal of FIG. 10A, which is a master signal, that is, the clock of the CPU 9a. Is performed at an appropriate timing.

As described above, the CPU 9a on the first gate side and the CPU 9b on the second gate side time-divisionally transmit the detection signals, and the article detection processing is performed by the CPU on the first gate side.
At 21a, the second gate side is independently performed by the CPU 21b, and the notification is performed by different lamps and buzzers. Therefore, it is possible to detect which gate the shoplifting has occurred so that it can be detected. The user can be notified in a distinguishable manner at which gate the shoplifting occurred. Therefore, the person who shoplifted can be appropriately detected.

Further, the determination process performed in each article detection process can also be performed accurately without being affected by random noise. In the following, only the first gate side will be described. In the same period as the sweep period of the detection signal transmitted from the first transmitting antenna 1a as shown in FIG. 6 ms
The signal level of the received signal from the receiving antenna 3 is sequentially stored in the RAM as level data via the A / D converter 47 every predetermined time Δt in the sweep period (S420-).
S470), whereby the level data when the detection signal of the same frequency is transmitted is stored for a plurality of sweep cycles (16 cycles in this embodiment). Then, the level data for 16 cycles corresponding to the detection signals of the same frequency are averaged (S240 to S280), and the first transmitting antenna 1a and the receiving antenna 3 are based on the respective average values (average data) D1 to D80. Between the resonance circuit Ma
It is determined whether or not the article M1 having 1 exists (S290).

Therefore, according to the shoplifting prevention apparatus of this embodiment, random noise occurs within the sweep frequency range (f1 to f2) of the detection signal, and as shown in FIG. Even if a large level change occurs in the level data input from the / D converter 47 to the CPU 21a, the calculated average data D1 to D80 do not have a significant effect, as shown in FIG. 7B. On the other hand, when the resonance circuit Ma1 (article M1) exists between the first transmitting antenna 1a and the receiving antenna 3, the level data corresponding to the detection signal of the same frequency continuously fluctuates greatly, As shown in FIG. 7B, the average data also largely changes from the steady value.

Therefore, according to the shoplifting prevention device of this embodiment, only the existence of the resonance circuit Ma can be accurately detected without being affected by the random noise, and the shoplifting action can always be accurately detected. It can be detected and notified. Further, in the shoplifting prevention device of the present embodiment, after the receiving device 7 is powered on and after the level data has been captured for 16 sweep cycles (S230: YES), 80 level data for one sweep cycle. Each time the data is fetched, the average data D1 to D80 are calculated using the level data for a total of 16 sweep cycles consisting of the level data for the current cycle and the level data for the immediately preceding 15 sweep cycles ( S240-S320).

That is, it is conceivable that the presence / absence of the resonance circuit Ma1 (article M1) may be determined by calculating the average data every time the level data for 16 sweep cycles is always fetched. The time interval for making the determination becomes large. On the other hand, according to the shoplifting prevention apparatus of this embodiment, after the average data is first calculated after the power is turned on, the oldest level data for one sweep cycle is discarded and the level data for the latest one sweep cycle is discarded. Since the average data D1 to D80 are calculated each time the data is taken in, stable determination can be made every sweep period, and the presence of the article M1 can be detected with good responsiveness.

Furthermore, in the shoplifting prevention device of this embodiment,
When the signal level of the reception signal is detected on the reception device 7 side, fi (= 10.7M) is detected from the detection signal from the DDS 29.
(Hz) a sine wave signal having a high frequency is always output, and the sine wave signal and the reception signal from the reception antenna 3 are mixed by the mixer 35, and the frequency of the reception signal is converted into the intermediate frequency fi, and the frequency conversion is performed. The received signal after is detected by the detector 4
I detect it in 1. That is, the shoplifting prevention device of the present embodiment adopts a so-called heterodyne method in which the frequency of the reception signal that periodically changes according to the frequency change of the detection signal is converted into a constant frequency fi and then the reception level is detected. are doing.

Therefore, according to the shoplifting prevention apparatus of this embodiment, the signal level of the received signal can be detected through the narrow band IF bandpass filter 37 that attenuates the frequency components other than the intermediate frequency fi, and eventually Since the reception level can be detected only for the frequency component of the detection signal actually transmitted at that time without detecting the reception level in the entire sweep frequency range (f1 to f2) of the detection signal, external noise can be detected. It is possible to more accurately determine the presence or absence of the article M1 having the resonance circuit Ma1 by minimizing the influence of the above.

Although the shoplifting prevention device which is an embodiment of the present invention has been described above, the present invention is not limited to this structure and can be implemented in various modes. For example, in the shoplifting prevention device, the CPU 9a of the first transmitting device 5a handles the processing as the synchronization signal generating means, but the CPU 21b of the receiving device 7 may perform the processing. In this case, the CPU 9a detects the fall of the synchronizing signal and sends the detection signal from the first transmitting antenna 1a.

Further, the permission signal generating means is also in charge of the C
You may change PU. For example, in the shoplifting prevention device, although the permission signal is generated by the CPU 21a,
When this is handled by the CPU 9b, the CPU 9b
After detecting the falling edge of the sync signal from the CPU 9a, the CPU b waits for at least the time (1.61 ms in the above example) required to complete the sweep of the detection signal on the first gate side. Then, after issuing the permission signal to the CPU 21b, the generation of its own detection signal, that is, the second sweep process may be started.

Alternatively, the sync signal may be generated from a different device. That is, a synchronization signal generator is separately provided, and the fall of the synchronization signal generated from the device is controlled by the CPU 9a.
(And the CPU 21a) may detect and send out the detection signal (and perform the first data fetching process). Similarly, the processing as the permission signal generating means may have another configuration.

Further, the structure may be such that both the synchronizing signal generating means and the permission signal generating means are combined. That is, one signal generator generates the synchronization signal and the permission signal separately,
The synchronization signal is the CPU 2 of the first transmitter 5a and the receiver 7.
For 1a, the permission signal is sent to the second transmitting device 5b and the CPU 21b of the receiving device 7. This makes it possible to easily drive the synchronization signal and the permission signal with the common clock oscillator.

Furthermore, the sweep time of the first transmitter 5a and the second sweep time
The sweep time of the transmitter 5b is common in the shoplifting prevention device, but may be different. Further, the change pattern of the detection signal may be changed irregularly instead of the linear pattern as shown in FIG. Or first
The transmitting device 5a and the second transmitting device 5b may have different change patterns. In any case, the article detection process on the receiving side is performed in synchronization with the transmission of the detection signal,
By outputting the frequency data corresponding to the change pattern to the SW 28, appropriate article detection can be performed as in the shoplifting prevention device.

In the above example, the falling edges of the sync signal and the enable signal are detected to synchronize the transmission and reception, but it is of course possible to detect the rising edge of the signal.
By positively utilizing this, the synchronization signal and the permission signal may be expressed by a common signal. For example, this common signal is
It is set to High at the timing from the fall of the synchronization signal to the fall of the permission signal, and it is set to Low at other timings. Then, the first sweep process may be started after the rise of this common signal, and the second sweep process may be started by detecting the fall of this common signal.

At this time, as a matter of course, the first data fetching process of the receiving device 7 starts upon detecting the rising edge of this common signal, and the second data fetching process starts the falling edge of this common signal. Detect and start. If the sweep time is made sufficiently smaller than the width of the common signal (the time from the rising edge to the falling edge), the shoplifting prevention device can be operated without considering the difference in the detection level of the rising edge or the falling edge of the common signal. As in the above, shoplifting can be properly detected.

In the shoplifting prevention device, the permission signal is generated for a predetermined time (1.61 m after the synchronization signal is received).
s) The processing is performed after a certain period of time, but instead of this, it may be generated when the first data acquisition processing is completed. By doing so, it is expected that the timing at which the permission signal is generated will not be constant with respect to the synchronization signal depending on the content of the processing and the conditions such as temperature. Since they are performed in synchronization, no problem occurs. Therefore, the same effect as that of the shoplifting prevention device can be obtained.

Further, if a high speed CPU may be used as the CPU on the receiver side, the CPUs 21a, 21a
The process of b may be performed by one CPU. In this case, this one CPU detects the falling edge of the synchronization signal, starts processing for one detection cycle, and receives the detection signal twice each detection cycle. Then, the level data from the A / D converter 47 is alternately stored in two different address spaces on the RAM, the average value for each same time is calculated for each, and the article is detected. Each has its own independent lamp or buzzer. It should be noted that when the time required to finish the article detection process for the first detection signal after the falling edge of the synchronization signal is detected, a permission signal is generated for the CPU 9b of the second transmission device 5b. , The transmission and reception on the second gate side are synchronized.

In this structure, the identification of which gate the article is detected is based on the detection signal received immediately after the synchronization signal or the detection signal received next.
That is, the detection is performed depending on which of the two address spaces the data is stored in. By doing so, the number of CPUs of the receiving device 7 is only one, and the configuration is simple. For example, the permission signal is sent from the CPU 21a to the CP.
The configuration for sending to the U21b, the SW28 for switching the frequency data from the CPUs 21a and 21b, and the like are unnecessary. If the duty ratio of the detection signal, that is, the length of the sweep time with respect to the detection cycle is set sufficiently shorter than 1/2, the time for performing the first (second) average value calculation processing and the like can be secured, Even a CPU that is not very fast can be used.

Also, in the case where three or more gates are provided for a store or the like having an entrance / exit wider than two gates, the shoplifting prevention device of the present invention can be easily changed only slightly. Applicable to For example, taking the case of three gates as an example, in addition to the configuration of the shoplifting prevention device, a second receiving device and a third notifying unit are further added, and at the entrance and exit, for example, the first transmitting device 5a and the receiving device. 7, the second transmitting device 5b, and the second receiving device are arranged in this order, and the first, second, and third gates are formed between these four devices. Then, the second receiving device detects the fall of the permission signal from the CPU 21a and performs the same article detection process as the process performed by the CPU 21b of the receiving device 7. In other words, the change of the shoplifting prevention device itself is to connect the two receiving devices so that the permission signal can be sent to the second receiving device, and
The transmitting antenna 1b need only be a directional antenna capable of transmitting a detection signal in at least both directions of the receiving device 7 and the second receiving device.

At this time, the detection signal emitted from the second transmitter 5b is simultaneously received by the receiver 7 and the second receiver, but the shoplifting of the second gate and the third gate can be identified. Can be detected and notified. That is, when shoplifting occurs at the third gate (second gate),
The change in the signal level due to the resonance circuit is detected by the second receiving device (reception device 7) and the notification operation is performed, but the reception device 7 (second receiving device) is detected because the distance to the resonance circuit is long. Can not. Therefore, shoplifting at the second gate and the third gate can be detected in a distinguishable manner. Also, the first gate and the second
Since the gates can be discriminated from each other, even if the shoplifting occurs in any of the three gates, it is possible to determine and notify each other so as to be distinguishable from each other.

When there are four gates, a fourth receiving device and a fourth notifying means may be further provided in addition to the configuration of the above-mentioned case where there are three gates. . That is, two shoplifting prevention devices of the present invention having a common detection cycle are installed (referred to as a first shoplifting prevention device and a second shoplifting prevention device, respectively), and the sweep time common to both devices is set to 1 /
The number is set to be shorter than 4, and the first shoplifting prevention device is additionally provided with a second permission signal generating means for issuing a second permission signal when a sufficient time has elapsed for the second data fetching process. On the other hand, the second shoplifting prevention device eliminates the synchronization signal generating means and uses the second permission signal instead of the synchronization signal to synchronize the sweep and the detection. Then, wherever the shoplifting occurs among the four gates, the shoplifting can be performed by appropriately identifying the shoplifting.

Even if the number of gates is five or more, the shoplifting prevention device according to the present invention can flexibly cope with the case where the number of gates is three or four, by appropriately combining the configuration changes. In the shoplifting prevention device,
A cable 59 is used as a transmission method of the synchronization signal and the permission signal.
Although the transmitters 5a and 5b and the receiver 7 are connected by a and 59b, they may be wireless. For example, the synchronization signal and the permission signal are ultrasonic waves, optical transmission / reception, or sweep frequency (f
1 to f2) other than radio waves may be transmitted.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a configuration of the present invention.

FIG. 2 is a block diagram showing a configuration of a shoplifting prevention device according to an embodiment.

FIG. 3 is a flowchart showing a first sweep process executed by the first transmitter.

FIG. 4 is a flowchart showing a first article detection process executed by the receiving device.

FIG. 5 is a flowchart showing a first data acquisition process executed in the first article detection process.

FIG. 6 is an explanatory diagram illustrating an operation of a first sweep process and a first article detection process.

FIG. 7 is an explanatory diagram showing the principle of detecting an article in the shoplifting prevention device of the present embodiment.

FIG. 8 is a flowchart showing a second sweep process executed by the second transmitter.

FIG. 9 is a flowchart showing a second data acquisition process executed in the second article detection process.

FIG. 10 is a timing chart showing a temporal relationship between a synchronization signal, two detection signals, and a permission signal.

[Explanation of symbols]

1a, 1b ... Transmitting antenna 3 ... Receiving antenna 5a, 5b ... Transmitting device 7 ... Receiving device 9a, 9b, 21a, 21b ... Microcomputer (CPU) 11a, 11b, 29 ... Direct digital synthesizer (DDS) 13a, 13b , 45 ... Low-pass filters 15a, 15b, 27 ... Variable attenuators 17a, 17b,
25, 31 ... Amplifier 23, 33 ... Bandpass filter 28 ... Switching circuit (SW) 35 ... Mixer 37 ... IF bandpass filter
39 ... IF amplifier 41 ... Detector 43 ... High-pass filter
47 ... A / D converter 49 ... Diode 51 ... Automatic gain control circuit
53 ... Comparators 55a, 55b ... Lamps 57a, 55b
Buzzer M1, M2 ... Product Ma1, Ma2
... LC resonant circuit

Claims (3)

[Claims] 1. A first transmitting antenna and a second transmitting antenna which are installed at a predetermined interval, a receiving antenna which is installed in the center of the first transmitting antenna and the second transmitting antenna, and which receives a predetermined command. First transmitting means and second transmitting means for transmitting a detection signal of a frequency corresponding to the command from the first transmitting antenna and the second transmitting antenna, respectively, and a synchronization signal at a constant cycle preset as a detection cycle. And a synchronization signal generating means for generating a frequency of the detection signal during a sweep time preset as a time shorter than 1/2 of the constant cycle each time the synchronization signal is received. The first command is to stop the transmission of the detection signal during the time period until the synchronization signal is received again.
First frequency control means for transmitting means, and the first transmitting antenna and the receiving antenna based on the signal level of the received signal from the receiving antenna during the sweep time each time the synchronizing signal is received. A first article detecting means for determining whether or not an article having a resonance circuit whose resonance frequency is set within the frequency range is present, and the first article detecting means determines that the article is present. A first notification means for notifying that the synchronization signal has been received, a permission signal generating means for generating a permission signal when the sweep time has elapsed after receiving the synchronization signal, and the sweep time of the sweep time each time the permission signal is received. During the period, the frequency of the detection signal is changed in a change pattern within a predetermined frequency range, and then the command to stop the transmission of the detection signal is issued during the time period until the permission signal is received again. Second frequency control means for two transmitting means, and the second transmitting antenna and the receiving antenna based on the signal level of the received signal from the receiving antenna during the sweep time after receiving the permission signal. And a second article detecting means for determining whether or not an article having a resonance circuit whose resonance frequency is set within the frequency range is present, and the second article detecting means for determining that the article is present. A shoplifting prevention device comprising: a second notifying means for notifying that the shoplifting has been performed. 2. The shoplifting prevention device according to claim 1, wherein when the first article detection means receives the synchronization signal, the first article detection means detects the signal level of the reception signal at predetermined time intervals during the sweep time. First level detecting means, first storing means for sequentially storing each signal level detected by the first level detecting means, and signal levels for a predetermined detection period stored in the first storing means, First average value calculating means for calculating each average value of the signal levels detected at the same time in each detection cycle, and whether or not the article exists based on the average value calculated by the first average value calculating means. If the second article detecting means receives the permission signal, the sweep operation is performed when the second article detecting means receives the permission signal. Time During the period, second level detecting means for detecting the signal level of the received signal at predetermined time intervals, second storage means for sequentially storing each signal level detected by the second level detecting means, and the second storage Second average value calculating means for reading out a signal level for a predetermined detection cycle stored in the means, and calculating each average value of the signal levels detected at the same time in each of the detection cycles, and the second average value calculating means. It is determined whether or not the article is present based on the average value calculated by, and when it is determined that the article is present, a second determination means that causes the second informing means to perform an informing operation is provided. Characteristic shoplifting prevention device. 3. The shoplifting prevention device according to claim 2, wherein the first level detection means and the second level detection means respectively include a first oscillator and a second oscillator whose oscillation frequencies are controllable, respectively. First frequency conversion means and second frequency conversion means for mixing the oscillation signals from the oscillator and the second oscillator with the reception signal to convert the frequency of the reception signal into different frequencies; and the first frequency conversion means and First frequency conversion control means and second frequency control means for controlling the oscillation frequencies of the first oscillator and the second oscillator, respectively, so that the frequency of the received signal converted by the second frequency conversion means is always a predetermined measurement frequency. The conversion control means, and the detection cycle that is the same as the cycle in which the frequency of the detection signal sent by the first frequency control means and the second frequency control means is changed, and within each detection cycle. Anti-shoplifting device characterized by comprising: a first detecting means and second detecting means for detecting the signal level of the output signal from the wave number conversion means as a signal level of the received signal.